Keratometry is a technique for correcting ametropy in an eyeball and consists in attaching to the outside of the cornea a corrective lense which was hitherto obtained by removing a cornea from a donor eyeball and processing the cornea to form therein:
an optical zone which has a lenticular shape of predetermined optical axis and is bounded by a convex front face and a concave rear face respectively having respective geometries determined on the one hand in relation to the possibility of applying the rear face of the optical zone closely against the cornea of the eyeball to be corrected (receiving eyeball), more particularly with coincidence between the optical axis and the visual axis of the receiving eyeball, and also in relation to predetermined optical characteristics in dependence on the correction to be applied to said eyeball, and
an anchoring zone having an annular shape of revolution around the optical axis and edging the optical zone in the direction away from the optical axis, for insertion into an annular incision in the cornea of the receiving eyeball.
In the prior art techniques the anchoring zone is very thick at the periphery of the lense and its insertion in the incision in the cornea of the receiving eyeball requires a deep incision parallel with the visual axis, and then a deep dissection parallel with the surface of the cornea. This is traumatic and moreover does not ensure the stable anchorage of the lense without a suture, except if the anchoring zone is large; moreover, the considerable thickness of the anchoring zone at the periphery of the lense causes, after its insertion in the cornea, a fillet of excess thickness in relation to the optical zone, and whatever care may be devoted to the production of the lense, i.e., the cutting of the cornea taken from the donor eyeball, it is practically impossible to obtain a regular transition between the lense and the cornea of the receiving eyeball on the surface and in depth around the lense. Moreover, at the surface the epithelium may increase in thickness and modify refraction, which makes this technique imprecise, as does possible mechanical distortion of the lense on insertion.